XDrawArc(3)

💅 NAME 💅

okay so bestie, welcome to the XDrawArc page — home of XDrawArc, XDrawArcs, and the XArc struct 💖 (yes, that's the draw arcs and arc structure trifecta, this is an XLIB FUNCTIONS moment, main character energy fr fr).

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✨ SYNTAX ✨

here's the summoning ritual, copy it exactly 👑

int XDrawArc(Display *display, Drawable d, GC gc, int x, int y, unsigned
       int width, unsigned int height, int angle1, int angle2);

int XDrawArcs(Display *display, Drawable d, GC gc, XArc *arcs, int
       narcs);

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🎀 ARGUMENTS 🎀

• angle1 — where the arc starts, measured from the three-o'clock position from the center. units are degrees * 64, no cap 🫶
• angle2 — the path and extent of the arc, relative to the start of the arc. also degrees * 64 ✨
• arcs — an array of arcs. it's giving plural 💅
• d — the drawable. that's the thing you're drawing on, periodt.
• display — the connection to the X server. your lil phone line to the server bestie ☎️
• gc — the GC. iconic, essential, we love her.
• narcs — how many arcs are in that array. count 'em. 🔢
• width, height — the width and height, which are literally the major and minor axes of the arc. big axis energy and little axis energy 🌸
• x, y — the x and y coordinates, relative to the origin of the drawable, specifying the upper-left corner of the bounding rectangle. yes, upper-LEFT, not the center, don't come for me 🙈

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🌈 DESCRIPTION 🌈

so XDrawArc draws one circular or elliptical arc, and XDrawArcs draws multiple circular or elliptical arcs — the plural version truly ate 💅. every arc is specified by a rectangle and two angles. the center of the circle or ellipse is the center of the rectangle, and the major and minor axes are specified by the width and height.

positive angles = counterclockwise motion 🌀, negative angles = clockwise motion. and if the magnitude of angle2 is greater than 360 degrees? XDrawArc or XDrawArcs truncates it to 360 degrees. it said "that's enough outta you" 💀.

lowkey important: angle1 and angle2 are in units of degrees * 64, not plain degrees. don't forget the 64 or your arc will be somewhere unhinged.

okay, math time, but make it cute 🧮 — for an arc specified as [x,y,width,height,angle1,angle2]:

• the origin of the major and minor axes is at [x+_____,y+______]
• the infinitely thin path describing the entire circle or ellipse intersects the horizontal axis at [x,y+______] and [x+width,y+______]
• and intersects the vertical axis at [x+_____,y] and [x+_____,y+height]

these coordinates can be fractional and so are not truncated to discrete coordinates. the path should be defined by the ideal mathematical path — we're being mathematically honest here ✨. for a wide line with line-width lw, the bounding outlines for filling are given by the two infinitely thin paths consisting of all points whose perpendicular distance from the path of the circle/ellipse is equal to lw/2 (which may be a fractional value — slay, fractions). the cap-style and join-style are applied the same as for a line corresponding to the tangent of the circle/ellipse at the endpoint 🎀.

now the spicy part 🌶️: for an arc specified as [x,y,width,height,angle1,angle2], the angles must be specified in the effectively skewed coordinate system of the ellipse (for a circle, the angles and coordinate systems are identical — lucky them). the relationship between these angles and angles expressed in the normal coordinate system of the screen (as measured with a protractor) is as follows:

skewed-angle=atan⎝tan(normal-angle)*______⎠+adjust

the skewed-angle and normal-angle are expressed in radians (rather than in degrees scaled by 64) in the range [0,2π], and where atan returns a value in the range [−_,_] and adjust is:

l l.  0    for normal-angle in the range [0,_] π    for normal-angle in the range [_,__] 2π   for normal-angle in the range [__,2π]

ngl that whole block is a mood, but it's the real formula, don't @ me 😭.

the pixel rules (important, pay attention bestie):

• for any given arc, XDrawArc and XDrawArcs do not draw a pixel more than once 👑
• if two arcs join correctly and the line-width is greater than zero and the arcs intersect, XDrawArc and XDrawArcs do not draw a pixel more than once either. team no double-drawing 🤝
• otherwise, the intersecting pixels of intersecting arcs are drawn multiple times. it's giving messy, but that's the spec 💀
• specifying an arc with one endpoint and a clockwise extent draws the same pixels as specifying the other endpoint and an equivalent counterclockwise extent — except as it affects joins. symmetric queen ✨

joining arcs, the lore 🦋:

• if the last point in one arc coincides with the first point in the following arc, the two arcs will join correctly.
• if the first point in the first arc coincides with the last point in the last arc, the two arcs will join correctly.
• by specifying one axis to be zero, a horizontal or vertical line can be drawn. line hack unlocked 🎉
• angles are computed based solely on the coordinate system and ignore the aspect ratio. periodt.

the GC components era 💅 — both functions use these GC components: function, plane-mask, line-width, line-style, cap-style, join-style, fill-style, subwindow-mode, clip-x-origin, clip-y-origin, and clip-mask. and they also use these GC mode-dependent components: foreground, background, tile, stipple, tile-stipple-x-origin, tile-stipple-y-origin, dash-offset, and dash-list. that's a lot of components and they're all equally important, we stan a thorough API 🫶

and finally: XDrawArc and XDrawArcs can generate BadDrawable, BadGC, and BadMatch errors. the trio of chaos 😭

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🧚 STRUCTURES 🧚

the XArc structure contains:

typedef struct {
     short x, y;
     unsigned short width, height;
     short angle1, angle2;             /* Degrees * 64 */
} XArc;

all x and y members are signed integers. the width and height members are 16-bit unsigned integers. you should be careful not to generate coordinates and sizes out of the 16-bit ranges, because the protocol only has 16-bit fields for these values 🔥 — this is a real warning, not a vibe, so like… respect the 16 bits bestie 🙏

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💀 DIAGNOSTICS 💀

• BadDrawable — a value for a Drawable argument does not name a defined Window or Pixmap. it's giving "who dis" 🙈
• BadGC — a value for a GContext argument does not name a defined GContext. same energy, wrong context 😭
• BadMatch — an InputOnly window is used as a Drawable. nope, not that kind of window 💅
• BadMatch — some argument or pair of arguments has the correct type and range but fails to match in some other way required by the request. so close and yet so far 💔

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🦋 SEE ALSO 🦋

• XDrawLine(3)
• XDrawPoint(3)
• XDrawRectangle(3)
• Xlib - C Language X Interface

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and that's the page babes 🫶 this whole thing comes to you straight from X Version 11, libX11 1.8.14 — go draw some arcs, you're gonna absolutely slay 💖✨🎀